1. Field of the Invention
The invention relates to a hybrid vehicle and a control method for the same. More specifically, the invention relates to a hybrid vehicle that travels using only power input to and output from a motor in an electric-powered travel mode, and travels using power output from an internal combustion engine and the power input to and output from the motor in a hybrid travel mode, and a control method for the same.
2. Description of Related Art
Japanese Patent Application Publication No. 2007-62640 (JP-A-2007-62640) describes an example of the hybrid vehicle. In the publication No. 2007-62640, when a target state of charge (SOC), which is the target state of charge of a secondary battery, is set, the hybrid vehicle travels in an HV mode where only power from a motor is used and an engine is stopped until the state of charge (SOC) of the secondary battery reaches the target SOC. After the SOC of the secondary battery reaches the target SOC, the hybrid vehicle travels in an HV mode where power from the engine and power from the motor are used. When the hybrid vehicle travels in the HV mode, the charging/discharging of the secondary battery is controlled so that the SOC of the secondary battery is equal to the target SOC. As a result, when the hybrid vehicle reaches a destination, the SOC of the secondary battery is equal to the target SOC. Thus, it is possible to set the target SOC taking into account the usage of electric power at the destination.
Recently, a so-called plug-in hybrid vehicle has been proposed. In the plug-in hybrid vehicle, while a system is in a stopped state, a secondary battery, which supplies electric power to a motor, is connected to an external power source, and is charged with electric power from the external power source. In the plug-m hybrid vehicle, each time the system is to be started, the secondary battery is charged. Therefore, in order to decrease the amount of electricity stored in the secondary battery (hereinafter, referred to as “charge amount”) by the time when the system is stopped, the hybrid vehicle generally travels with priority being given to an electric-powered travel mode where the engine is stopped and only the power from the motor is used. In the case where a driver depresses an accelerator pedal to a large extent and the hybrid vehicle is required to travel with large driving power while the hybrid vehicle is traveling in the electric-powered travel mode, the required driving power cannot be provided by using only the power from the motor, and therefore, a control is switched so that the engine is started and the hybrid vehicle travels with the required driving power using the power from the engine and the power from the motor. Then, when the charge amount has decreased to a certain low level, a target charge amount is set to the charge amount at that time, and thus, the charge amount of the secondary battery is maintained. In addition, the control is switched so that the hybrid vehicle travels with priority being given to a hybrid travel mode where the power from the engine and the power from the motor are used. Thus, in the plug-in hybrid vehicle, it is effective to provide a mode changeover switch that switches a travel mode between an electric-powered travel priority mode where the hybrid vehicle travels with priority being given to the electric-powered travel mode, and a hybrid travel priority mode where the hybrid vehicle travels with priority being given to the hybrid travel mode, taking into account the usage of electric power at the destination, as well as in the above-described hybrid vehicle. However, because the purposes of the travel modes are different from each other, the management of the charging/discharging of the secondary battery during the travel control in the electric-powered travel priority mode is different from the management of the charging/discharging of the secondary battery during the travel control in the hybrid travel priority mode. Therefore, when the mode changeover switch is operated while the engine is being operated, an operation point for the engine may be suddenly changed due to a sudden change in the charging/discharging of the secondary battery, and thus, a driver or an occupant may feel discomfort. Also, when the mode changeover switch is not operated but the travel mode is switched while the engine is being operated, the operation point for the engine may be suddenly changed, and thus, the driver or the occupant may feel discomfort.